1. Field of the Invention
The present invention relates to a pattern inspection system.
The pattern inspection system can be used to inspect patterns of leads on a printed circuit board (PCB), and patterns of a semiconductor chip, etc.
2. Description of the Related Arts
Recently, an improvement in the inspection of patterns on a PCB has been urgently sought, to improve the reliability of system products provided with such PCBs.
Such inspections were carried out by visual observation with a microscope, but the use of extremely complex and miniaturized patterns, and the requirements for reductions in labor and production costs, has led to attempts to develop an automatic inspection system therefor.
JPP No. 58-207633 discloses a system for automatically inspecting patterns on a PCB. In this system, the patterns are optically scanned and, converted into electrical signals. The electrical signals are encoded into binary data, and the binary data is stored in a memory. The binary pattern data is then applied to spatial filters having specific characteristics to extract features of the patterns and detect any abnormalities in the patterns. More specifically, the above spatial filters detect faults by defining shapes which occur in the patterns to be inspected. The binary pattern data is consecutively compared with the spatial filters. If overlapping portions are detected between the input binary pattern data and one of the spatial filters, the system defines those overlapping portions as pattern error portions.
The above spatial filters are designed to act only with a specific pattern and, as a result, the system can not be used to inspect a variety of patterns. Thus, the application of the system is limited. In addition, each spatial filter has a two dimensional shape, and it is difficult to optimize the arrangement of the spatial filter for each pattern. Misjudgments are liable to occur during the inspection.
JPP No. 59-74627 also discloses a method and apparatus for inspecting patterns of photomasks used for PCBs. The apparatus includes an optical means, a scanner, a binary coding means, a memory, an inspection means, and a display. In this apparatus, the inspection means is provided with a picture element type length measurement means having radial directional scales. The length measurement means is applied on a matrix data plane in the memory stored binary coded pattern scan data, to obtain a width of the pattern on the PCB.
The apparatus does not position a center of the width of the pattern. As a result, a correct inspection can not be realized. Also, the apparatus does not use a reference dictionary for comparing actual pattern data. Thus, there is a low inspection accuracy. In addition, the binary coded pattern scan data is not classified by the validity of the width of the pattern. This results in a considerable lengthening of the inspection time and limits the invention to general inspection technology. Furthermore, this apparatus can not detect a two dimensional fault of the pattern, for example, a break of the pattern in a longitudinal direction, and a narrow space between adjacent patterns, etc.